摘要
通过对西湖凹陷天台反转带花港组20口井地层水地球化学特征进行研究,进一步揭示地层水成因、来源以及保存条件。研究结果表明,花港组地层水离子组成以Cl^(−)、Na^(+)、Ca^(2+)以及HCO3^(−)为主,其中Na^(+)和Cl^(−)浓度与矿化度(TDS)之间呈现较好的线性关系,具有高浓缩地层水的特征。水型以氯化钙Ⅳ型和Ⅴ型为主;钠氯系数和脱硫系数均较小,远低于海水;钙镁系数高于深层水,均指示花港组地层封闭性好,处于交替停滞带,有利于油气的聚集与保存。Na^(+)轻微亏损主要受钠长石化作用影响;Ca^(2+)富集除了钠长石化作用外,有机质成熟过程中伴生的有机酸,对长石和含钙矿物的溶蚀作用,也促进地层水中Ca^(2+)的富集;Mg2+亏损可能与高岭石、绿泥石以及白云岩化紧密相关。花港组地层水来源于陆相沉积水,受沉积环境、水-岩反应、蒸发浓缩作用以及流体混合作用共同控制,表现出富Ca^(2+),贫Mg2+,略微贫Na^(+)的特点。
Based on the geochemical features of the formation water in Huagang Formation collected from 20 wells on the Tiantai structure of Xihu Depression,the genesis,source and preservation conditions of the formation water are discussed in this paper.The water is dominated by Cl^(−),Na^(+),Ca^(2+)and HCO3^(−).And the concentrations of Na^(+)and Cl^(−)show an obvious linear relationship with TDS which suggests a kind of highly concentrated formation water.The water is mainly of types CaCl2ⅣandⅤ.r(Na^(+))/r(Cl^(−))and 100×(rSO42−)/r(Cl^(−))are lower than those in seawater;while r(Ca^(2+))/r(Mg2+)are higher in deep water.All of these features indicate that the Huagang Formation has effective sealing capability and is deposited in an alternative stagnation zone,which is conducive as well to oil and gas accumulation and preservation.The slight loss of Na^(+)is mainly caused by albitization.In addition to the formation of sodium feldspar,organic acids associated with the maturation of organic matter and the dissolution of feldspar and calcium-bearing minerals,also promoted the enrichment of Ca^(2+)in the formation water.The deficiency of Mg2+may be closely related to the formation of kaolinite and chlorite in addition to dolomitization.The formation water of Huagang Formation originally came from land water and therefore is controlled by sedimentary environment,water-rock reaction,evaporation and concentration and fluid mixing characterized by rich Ca^(2+),poor Mg2+and slightly poor Na^(+).
作者
徐波
XU Bo(CNOOC EnerTech-Drilling&Production Co.CNOOC Central Laboratory(shanghai),Shanghai 200941,China)
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2021年第3期62-71,共10页
Marine Geology & Quaternary Geology
基金
“十三五”国家科技重大专项“东海深层低渗-致密天然气勘探开发技术”(2016ZX05027-001)。
关键词
地层水
地球化学特征
保存条件
水-岩作用
氢、氧同位素
西湖凹陷
花港组
formation water
geochemical characteristics
preservation condition
water-rock interaction
deuterium and oxygen isotopes
Xihu Depression
Huagang Formation
